Resume bounded C# origin classification (#5348)

[Widthdom]

Large indexed C# files can exhaust the origin-classification prefix while regex scanning completes. Add explicit --origin-passes (1–16, default 1) to search, audit and regex find so successive windows carry the shared lexical state forward. Each pass classifies at most 4,096 new lines and reads at most 8 Mi characters and 128 chunks, including overlap. Generation changes or conflicting overlap discard provisional state; missing or malformed context remains unknown. Find diagnostics distinguish exhausted budgets and give bounded retry guidance, with pass settings bound to cursor and recipe replay.

The original 6,299-line reproduction changes from 243 code / 111 unknown occurrences and exit 11 to 353 code / 0 unknown with two passes and authoritative completion. The remaining occurrence is non-code. The same counts and exit statuses were also verified against the indexed 6,305-line version of the fixture.

Validation:

• Full Release solution suite before the overlap review fix (serial MSBuild, shared compilation disabled): net8 — 12,521 passed, 9 skipped; net9 — 12,027 passed, 435 skipped; 0 failures on both runtimes.
• After the overlap fix and integration with origin/main (f0889b95b): 344 targeted Release tests passed on each of net8.0 and net9.0, including shared classification, continuation, help, completion and the incoming C# workspace expansion fixtures. The new boundary regression was confirmed failing before the fix; matching-overlap and completed-interpolation controls also pass.
• make lint, bilingual fragment validation and git diff --check passed. The CI whitespace failure in the continuation test initializers is fixed.
• Post-commit Debug CLI build passed with 0 warnings/errors; root and workspace index checks are healthy with complete reference coverage.
• Codex adversarial review completed, including the main integration and CI formatting repair. Final result: No blocking/actionable issues found.

Updated the English/Japanese user, developer, testing and find-control documentation. Changelog fragment: changelog.d/unreleased/5348.fixed.md. No changes to agent instruction files or CHANGELOG.md.

Fixes #5348

Follow-up: #5357.